In the world of directional drilling, the term "medium radius" refers to a specific type of well trajectory characterized by a moderate rate of deviation. This rate is typically defined as between 8 and 12 degrees of change in wellbore direction for every 100 feet of drilled depth.
Why is Medium Radius Important?
Medium radius wells offer a balance between controlled deviation and efficient drilling. They are commonly employed when:
Well Deviation Change at 8° per 100 ft:
A well deviation change of 8 degrees per 100 feet falls within the typical range for medium radius wells. This means that for every 100 feet drilled vertically, the wellbore will change direction by 8 degrees.
Visualizing the Deviation:
Imagine a straight line representing the vertical wellbore. As drilling progresses, the wellbore begins to deviate from this straight path. With an 8° per 100 ft deviation, the wellbore will gradually curve away from the vertical line, forming a smooth arc with a specific radius.
Applications of Medium Radius Wells:
Medium radius wells are commonly used in various drilling scenarios, including:
Conclusion:
Medium radius wells, with their characteristic deviation rates, provide a valuable tool for navigating complex subsurface environments. By balancing controlled deviation and drilling efficiency, they offer a practical and effective solution for reaching targeted formations while maintaining wellbore stability. The understanding of medium radius concepts and their application is crucial for optimizing well planning and execution in various drilling scenarios.
Instructions: Choose the best answer for each question.
1. What is the typical deviation rate for a medium radius well?
a) 2-4 degrees per 100 feet
Incorrect. This range is typical for low-radius wells.
b) 8-12 degrees per 100 feet
Correct. This is the standard range for medium radius wells.
c) 15-20 degrees per 100 feet
Incorrect. This range is typical for high-radius wells.
d) More than 20 degrees per 100 feet
Incorrect. This deviation rate would be considered extremely high.
2. Why are medium radius wells beneficial for targeting specific subsurface horizons?
a) They allow for rapid drilling and reach the target quickly.
Incorrect. While they are efficient, their primary benefit is controlled deviation.
b) They can navigate complex formations with minimal deviation.
Incorrect. This is more applicable to low-radius wells.
c) They maintain a controlled deviation rate to reach the target accurately.
Correct. Their moderate deviation allows for precise targeting.
d) They are the most cost-effective option for all drilling scenarios.
Incorrect. The cost-effectiveness depends on the specific drilling scenario.
3. Which of the following is NOT a reason why medium radius wells are considered efficient?
a) They require less complex drilling equipment.
Incorrect. This is a benefit of medium radius wells.
b) They can be drilled faster than high-radius wells.
Incorrect. This is a benefit of medium radius wells.
c) They often require multiple drilling stages to reach the target.
Correct. They are often more efficient than high-radius wells due to simpler equipment and faster drilling times.
d) They minimize drilling costs compared to other well types.
Incorrect. This is a benefit of medium radius wells.
4. What is the primary advantage of medium radius wells in terms of wellbore stability?
a) They create a wider wellbore, improving stability.
Incorrect. Wellbore diameter is determined by other factors.
b) They minimize sudden changes in wellbore pressure and stress.
Correct. Controlled deviation prevents sudden shifts in pressure and stress, promoting stability.
c) They allow for the use of stronger casing materials for increased stability.
Incorrect. Casing selection is influenced by other factors.
d) They are less susceptible to wellbore collapse due to their steeper angle.
Incorrect. The angle can actually increase the risk of collapse in some cases.
5. In which of the following applications are medium radius wells commonly used?
a) Shallow water drilling for oil and gas.
Incorrect. While they can be used in shallow water, they are more common for moderate depths.
b) Horizontal drilling for unconventional resources.
Incorrect. Horizontal drilling typically involves higher deviation rates.
c) Geothermal energy development.
Correct. Medium radius wells are often employed in geothermal energy extraction.
d) All of the above.
Incorrect. Medium radius wells are not typically used for horizontal drilling in unconventional resources.
Scenario:
You are planning a well to target a reservoir located 3000 feet below the surface with an inclination of 25 degrees. You decide to use a medium radius trajectory with a deviation rate of 10 degrees per 100 feet.
Task:
Instructions:
1. Total Horizontal Displacement (MD): * **Inclination angle:** 25 degrees * **Vertical depth:** 3000 feet * **Total deviation:** 10 degrees per 100 feet * 30 (100-foot intervals) = 300 degrees * **Horizontal displacement:** 3000 * tan(25) = 1400 feet (approximately) 2. Measured Depth (MD): * **Vertical depth:** 3000 feet * **Total deviation:** 300 degrees * **Measured depth:** 3000 / cos(25) = 3314 feet (approximately)
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